难动用煤层气资源的高产开采技术研究——论煤层气资源的特殊性及其开发工程中的“窗-尾效应”

Produce high rate gas from poor CBM reservoir-Study on CBM resource types and “Window-Longtail Effects”of reservoir during delivering gas

针对中国煤层气产业发展中,工程成功率和产量达成率双底以及开采难动用资源缺乏有效技术的两大难题,提出了解决两大难题的基本技术思路,建立了1套新的资源认识标准,并在这个标准指导下探讨如纠偏并设计更有效的开发技术路径和实施办法。研究发现了煤层气在赋存规律和开采技术要求上不同于其他天然气资源的三大特殊性,第一"非气",典型意义上的煤层气以特殊的固流体状态赋存,独立相态的气体资源是不存在的,依据耦合动力的不同把煤层气资源分为四大类;第二"育采",开采煤层气从来都不是直接采气,采气之前必须先通过解构工程把气培育出来,要么先"采水(排水)",要么先"采煤(掏煤)";第三"窗-尾效应",难动用煤层气资源的开采工艺的有效性取决于储层改造"时间窗"和排水"长尾"的管控效率。

It is found that there are two difficult problems in China CBM industry.The one is that not only the success rate of drilling and fracking is very low but also gas rates from more than 50% of those producing wells are far less than they are originally designed. The other is that almost all the production activities happen in a very concentrated small area,leaving more than 80% of China CBM resources far away from commercial potentials.A new model of CBM resource classification is established after a full discussion is made on how a soluid of coal-water-gas is built in the long geology history.And technologies applicable to produce gas from the 4 types of reserves in the model is accordingly recommended.Further studies in this paper concludes that CBM resources are different from other natural gas by three aspects.Firstly it is ＂Non-gas＂in underground.Typical CBM is presented in four kinds of Soluids,in which coalwater-gas are coupled together driven by a combination energy of ＂pressure＂and ＂stress＂. Secondly gas has to be＂Separated and Fostered＂before it is drained to the surface.Actually a real independent gas flow cannot be normally delivered from seam until an effective process of ＂dewater＂or ＂de-coal＂is done. Thirdly there is a strong ＂windowlongtail effects＂in poor CBM reservoir. No appreciable gas could be drained if there is no good engineering controlover ＂time window＂on reservoir stimulation,neither is there any sustainable gas flow if＂pumping longtail＂is not well managed.